Ball grid array package that includes a collapsible spacer for separating die adapter from a heat spreader

ABSTRACT

A ball grid array package is manufactured by mounting a semiconductor die to a first surface of a substrate and mounting a die adapter to the semiconductor die. The semiconductor die is wire bonded to ones of conductive traces of the substrate. A collapsible spacer is mounted to the substrate and the substrate is releasably clamped to an upper side of a mold cavity. A heat spreader and at least one collapsible spacer are placed in the mold cavity such that the collapsible spacer is disposed between the heat spreader and the substrate. A molding compound is molded in the mold, thereby molding the semiconductor die, the substrate, the wire bonds, the die adapter, the at least one collapsible spacer and the heat spreader into the molding compound to provide a molded package. A ball grid array is formed on a second surface of the substrate, bumps of the ball grid array being electrically connected to the conductive traces and the integrated circuit package is singulated.

CROSS REFERENCE TO RELATED APPLICATION

This is a Divisional Application of U.S. patent application Ser. No.10/643,961, filed Aug. 20, 2003, and issued as U.S. Pat. No. 6,987,032,which is a continuation-in-part of U.S. patent application Ser. No.10/323,657, entitled Process For Manufacturing Ball Grid Array Package,filed Dec. 20, 2002, and issued as U.S. Pat. No. 6,979,594, which is acontinuation-in-part of U.S. patent application Ser. No. 10/197,832entitled Improved Ball Grid Array Package, filed Jul. 19, 2002, andissued as U.S. Pat. No. 6,800,948.

FIELD OF THE INVENTION

The present invention relates in general to integrated circuitpackaging, and in particular to an improved ball grid array (BGA)package with enhanced thermal characteristics and a unique method ofmanufacturing the ball grid array package.

BACKGROUND OF THE INVENTION

High performance integrated circuit (IC) packages are well known in theart. Improvements in IC packages are driven by industry demands forincreased thermal and electrical performance and decreased size and costof manufacture.

In general, array packaging such as Plastic Ball Grid Array (PBGA)packages provide a high density of interconnects relative to the surfacearea of the package. However, typical PBGA packages include a convolutedsignal path, giving rise to high impedance and an inefficient thermalpath which results in low thermal dissipation performance. Withincreasing package density, the spreading of heat generated by thepackage is increasingly important.

Reference is made to FIG. 1, which shows an elevation view of aconventional PBGA package indicated generally by the numeral 20. ThePBGA package 20 includes a substrate 22 and a semiconductor die 24attached to the substrate 22 by a die adhesive. Gold wire bonds 26electrically connect the die 24 to metal traces on the substrate 22. Thewire bonds 26 and die 24 are encapsulated in a molding compound 28.Solder balls 30 are disposed on the bottom surface of the substrate 22for signal transfer. Because of the absence of a thermal path away fromthe semiconductor die 24, thermal dissipation in this package is poor.

Variations to conventional BGA packages have been proposed for thepurpose of increasing thermal and electrical performance. One particularvariation includes the addition of a metal heat spreader to the package,as shown in FIG. 2 which shows an elevation view of a PBGA package 20 ofthe prior art including the heat spreader, indicated by the numeral 32.In general, the metal heat spreader is fixed to the molded package. Thispackage suffers disadvantages, however, as heat must be dissipated fromthe semiconductor die 24, through the molding compound 28 and thenthrough the heat spreader 32.

It is therefore an object of an aspect of the present invention toprovide a process for manufacturing a BGA package with a heat spreaderthat obviates or mitigates at least some of the disadvantages of theprior art.

SUMMARY OF THE INVENTION

In one aspect, a process for manufacturing an integrated circuit packageis provided. The process includes mounting a semiconductor die to afirst surface of a substrate and mounting a die adapter to saidsemiconductor die. The semiconductor die is wire bonded to ones ofconductive traces of said substrate and at least one collapsible spaceris mounted to at least one of a heat spreader, said die adapter and saidsubstrate. One of the heat spreader and said substrate are placed in amold cavity and the other of said heat spreader and said substrate isclamped to a die of said mold cavity, such that said collapsible spaceris disposed between said heat spreader and said substrate. A moldingcompound is molded in the mold, thereby molding the semiconductor die,the substrate, the wire bonds, said die adapter, said at least onecollapsible spacer and said heat spreader into the molding compound toprovide a molded package. A ball grid array is formed on a secondsurface of said substrate, bumps of said ball grid array beingelectrically connected to said conductive traces and the integratedcircuit package is singulated.

In another aspect, a process for manufacturing a plurality of integratedcircuit packages comprises mounting a plurality of semiconductor dice toa first surface of a substrate array and mounting a plurality of dieadapters to said semiconductor dice such that each one of said dieadapters is mounted to a corresponding one of said semiconductor dice.The semiconductor dice are wire bonded to ones of conductive traces ofsaid substrate array and a collapsible spacer array is mounted to one ofa heat spreader array and said substrate array. One of said heatspreader array and said substrate array is placed in a mold cavity andthe other of said heat spreader array and said substrate array isreleasably clamped to a first die of said mold such that saidcollapsible spacer array is disposed between said heat spreader arrayand said substrate array. A molding compound is molded in the mold,thereby molding the semiconductor dice, said substrate array, said wirebonds, said die adapters, said collapsible spacer array and said heatspreader array into the molding compound to provide an array of moldedpackages. A plurality of ball grid arrays are formed on a second surfaceof said substrate array, bumps of said ball grid arrays beingelectrically connected to said conductive traces and each integratedcircuit package is singulated from said array of molded packages.

In another aspect, there is provided an integrated circuit package. Theintegrated circuit package is a ball grid array package that includes asubstrate that has a plurality of conductive traces. A semiconductor dieis mounted to a first surface of the substrate and a die adapter ismounted to the semiconductor die. A plurality of wire bonds connect thesemiconductor die and ones of the conductive traces. A heat spreader isdisposed proximal to and spaced from the die adapter by at least onecollapsible spacer. A molding compound encapsulates the semiconductordie, the wire bonds, the die adapter and the collapsible spacer betweenthe substrate and the heat spreader. A ball grid array is disposed on asecond surface of the substrate, bumps of the ball grid array beingelectrically connected to the conductive traces.

Advantageously, a heat spreader is incorporated into the BGA packageduring molding. The heat spreader is prepared and placed in the mold andis incorporated into the package by molding. An array of heat spreadersis placed in the mold and molded with a substrate array such that aplurality of packages including heat spreaders are manufactured in asingle mold shot.

A thermal path is provided from the semiconductor die, through the dieadapter and the collapsible spacer and to the heat spreader. Also, theheat spreader is effectively pressed against the lower mold die surfaceduring molding, thereby inhibiting mold flash on the outer side of theheat spreader. The incorporation of a deformable material (collapsiblespacer) that is stable at molding temperature, provides a compliantlayer between the substrate and the heat spreader and between thesemiconductor die and the heat spreader. Thus, the heat spreader ispressed against the lower mold die, maintaining the heat spreader incontact with the lower mold die during molding and reducing mold flash.

In another aspect, ground bonds are provided between the semiconductordie and the die adapter. Thus, a ground path is provided through the dieadapter, the collapsible spacer in contact with the die adapter, theheat spreader and the collapsible spacers in contact with the substrate.Advantageously, better signal layout on the substrate can be achievedand better wire looping control is provided. Also, ground wire length isreduced.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood with reference to the followingdescription and to the drawings, in which:

FIG. 1 shows an elevation view of a conventional plastic ball grid arraypackage;

FIG. 2 shows an elevation view of a prior art plastic ball grid arraypackage including a heat spreader;

FIGS. 3A to 3K show processing steps for manufacturing a ball grid arraypackage, in accordance with one embodiment of the present invention;

FIG. 4 shows a mold including molding dies and a mold cavity for moldingthe ball grid array package according to an embodiment of the presentinvention;

FIG. 5 shows a ball grid array package manufactured in accordance withan alternative embodiment of the present invention;

FIGS. 6A to 6J show processing steps for manufacturing a ball grid arraypackage, in accordance with another embodiment of the present invention;and

FIGS. 7A to 7J show processing steps for manufacturing a ball grid arraypackage, in accordance with yet another embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference is now made to FIGS. 3A to 3K to describe a process formanufacturing a ball grid array package, according to an embodiment ofthe present invention. To simplify the description, the numerals usedpreviously in describing FIG. 1 will be used again after raising thenumerals by 100 where parts to be described correspond to parts alreadydescribed.

Referring to FIG. 3K, the ball grid array package is indicated generallyby the numeral 120. The package 120 includes a substrate 122 that has aplurality of conductive traces. A semiconductor die 124 is mounted to afirst surface of the substrate 122 and a die adapter 134 is mounted tothe semiconductor die 124. A plurality of wire bonds 126 connect thesemiconductor die 124 and ones of the conductive traces. A heat spreader132 is disposed proximal to and spaced from the die adapter 134 by atleast one collapsible spacer 136. A molding compound 128 encapsulatesthe semiconductor die 124, the wire bonds 126, the die adapter 134 andthe collapsible spacer 136 between the substrate 122 and the heatspreader 132. A ball grid array 130 is disposed on a second surface ofthe substrate 122, bumps of the ball grid array 130 being electricallyconnected to the conductive traces.

The process for manufacturing the ball grid array package 120, accordingto one embodiment of the present invention, will now be described inmore detail. Referring to FIG. 3A, the substrate 122 of a BT resin/glassepoxy printed circuit board with conductive traces for signal transferis shown. A solder mask is disposed on the lower surface of thesubstrate, with portions of the conductive traces (interconnects)exposed. The substrate 122 is in the form of an array strip forproducing a number of BGA units. Three such units are depicted in anarray in FIG. 3A.

A singulated semiconductor die 124 is conventionally mounted to an uppersurface of the substrate 122 using a suitable die attach adhesive (FIG.3B). In the present embodiment, the semiconductor die 124 is attachedusing an epoxy and the epoxy is cured.

A die adapter 134 is mounted to the semiconductor die 124 using athermally conductive adhesive for conducting heat from the semiconductordie 124 to the adapter 134 (FIG. 3C). In the present embodiment, the dieadapter 134 is copper.

The semiconductor die 124 has a conductive pad array formed thereon andwire bonds 126 are bonded between the conductive pads of the array andthe conductive traces on the substrate 122 using conventional wirebonding techniques (FIG. 3D). Ground wire bonds 138 are also bondedbetween pads of the array and a ground pad on the substrate 122.

The heat spreader 132 is manufactured in the form of an array frame thatis compatible with the substrate array 122 (FIG. 3E). In the presentembodiment the heat spreader is a copper strip that is etched to formthe array frame. The array frame includes a number of heat spreaders 132joined together by partially-etched tie-bars. Three such heat spreadersare depicted in FIG. 3E.

A plurality of collapsible spacers 136 are mounted to the substrate 122.In the present embodiment, the collapsible spacers 136 are manufacturedin the form of an array that is compatible with the substrate array 122and the heat spreader 132 (FIG. 3F). The collapsible spacers 136 arecomprised of a solder preform of a plurality of substantially sphericalballs connected together by tie bars. The collapsible spacers 136 aremounted to the substrate 122 using epoxy. It will be appreciated thatsome of the collapsible spacers 136 are mounted directly on thesubstrate 122 and other collapsible spacers 136 are mounted tocorresponding die adapters 134 (FIG. 3G).

The heat spreader 132, in the array format, is placed in the bottom ofthe die cavity, on the lower surface of the mold. Features of the moldcavity and the frame are designed such that the heat spreader 132 alignswith the substrate 122 in the die cavity. The substrate array strip 122is clamped to a surface of an upper mold die, in the mold cavity suchthat the semiconductor die 124, the die adapter 134 and the collapsiblespacers 136 protrude from the substrate 22 into the mold cavity. Thecollapsible spacers 136, in the array format, are thus disposed betweenthe heat spreader 132 and the substrate 122 (FIG. 3H). A suitable moldincluding the molding dies and mold cavity is shown in FIG. 4.

Molding using a molding compound 128 in the mold cavity follows. Duringmolding, the collapsible spacers 136 are compressed between thesubstrate 122 and the heat spreader 132 and between the die adapter 134and the heat spreader 132, causing deformation of the collapsiblespacers 136 (FIG. 3I). The molding compound 128 encapsulates the wirebonds 126, the semiconductor die 124, the die adapter 134, and thecollapsible spacer 136 between the heat spreader 132 and the substrate122, and joins the heat spreader 132 to the remainder of the package120. The heat spreader 132 is thereby pressed against the lower surfaceof the mold in the die cavity.

After removing the package 120 from the mold, the solder balls 130, alsoreferred to as solder bumps, are formed on the lower surface of thesubstrate 122 by conventional positioning (FIG. 3J). To attach thesolder balls 130, a flux is added to the balls prior to placement and,after placement the solder balls 130 are reflowed using known reflowtechniques. The solder balls are thereby connected to the conductivetraces of the substrate 122 and through the wire bonds 126 to thesemiconductor die 124. The solder balls 130 provide signal and powerconnections as well as ground connections for the semiconductor die 124.

Singulation of the individual BGA unit from the array strip is thenperformed either by saw singulation or die punching, resulting in theconfiguration shown in FIG. 3K. Thus, the individual BGA package isisolated from the strip.

Reference is now made to FIG. 5 to describe an alternative embodiment ofthe ball grid array package 120 according to the present invention. Theprocess steps for manufacturing the ball grid array package 120 of FIG.5 are similar to the process steps for manufacturing the ball grid arraypackage of FIG. 3J, and therefore these process steps need not befurther described herein.

During wire bonding of the package shown in FIG. 5, wire bonds 126 arebonded between the conductive pads of the array and the conductivetraces of the substrate 122 using conventional wire bonding techniques,as described with reference to FIG. 3D. Ground wire bonds 138, however,are bonded between pads of the array and a surface of the die adapter134. A ground path is provided as the collapsible spacers 136 thatcontact the heat spreader 132 and the substrate 122, contact ground padson the substrate 122. Thus, the ground path is provided through the dieadapter 134, the collapsible spacer 136 in contact with the die adapter134, the heat spreader 132 and the collapsible spacers 136 in contactwith the ground pads of the substrate 122.

Reference is now made to FIGS. 6A to 6J to describe a process formanufacturing the ball grid array package 120, in accordance withanother embodiment of the present invention. FIGS. 6A to 6E are similarto FIGS. 3A to 3E and therefore need not be further described herein. InFIG. 6F, however, the collapsible spacers 136 are mounted to the heatspreader 132, rather than the substrate. The heat spreader 132, in thearray format, is then placed in the bottom of the die cavity, on thelower surface of the mold such that the collapsible spacers 136 protrudeinto the mold cavity. Features of the mold cavity and the frame aredesigned such that the heat spreader 132 aligns with the substrate 122in the die cavity. The substrate array strip 122 is clamped to a surfaceof an upper mold die, in the mold cavity such that the semiconductor die124 and the die adapter 134 protrude from the substrate 22 into the moldcavity. The collapsible spacers 136, in the array format, are thusdisposed between the heat spreader 132 and the substrate 122 and betweenthe heat spreader and the die adapter (FIG. 6G). FIGS. 6H to 6J aresimilar to FIGS. 3I to 3K and therefore need not be further describedherein.

Alternative embodiments and variations are possible. For example, ratherthan placing the heat spreader 132 in the bottom of the mold cavity andclamping the substrate 122 to the top mold die, the substrate 122 can beplaced in the bottom of the mold cavity and the heat spreader 132clamped to the top of the mold die. FIGS. 7A to 7J show the processingsteps for manufacturing a ball grid array according to one embodiment ofthe present invention. FIGS. 7G and 7H show the substrate 122 disposedin the bottom of the mold cavity and the heat spreader 132 clamped tothe top mold die (FIG. 7H).

In another alternative, the collapsible spacers 136 are individuallyplaced on the substrate 122 and die adapter 134 or on the heat spreader132, rather than being manufactured in the form of an array (FIGS. 7A to7J). In the embodiment shown in FIGS. 7A to 7J, the collapsible spacers136 are placed in the appropriate position on the substrate 122 and dieadapters 134 with pre-dispensed flux using pick and place technology,followed by solder reflow. In still another alternative embodiment,epoxy is pre-applied to the substrate 122 and the die adapter 134 or onthe heat spreader 132, the collapsible spacers 136 are placed using pickand place technology and the epoxy is cured.

Other alternative embodiments and variations are also possible. Forexample, rather than etching a copper strip to prepare the array frameof heat spreaders 132, the frame can be manufactured by metal stamping.Also, the heat spreader is not limited to copper as other suitable heatspreader materials are possible and will occur to those skilled in theart. In the above-described embodiments, the collapsible spacers aremounted to the substrate or the heat spreader using epoxy, however othermeans for mounting the collapsible spacers are possible. For example,the collapsible spacers can be mounted using solder reflow technique.Also, the collapsible spacers are not limited to solder preform as othersuitable materials can be employed, including for example, low modulusconductive polymer such as silicone or a thermoplastic material with lowmodulus such as polycarbonate. The die adapter 134 is not limited tocopper as other suitable materials can be used. For example, the dieadapter can be constructed of silicon, ceramics and other metals. In theembodiment shown in FIG. 5, the die adapter is constructed of a materialsuitable for wire bonding, such as silver plated, or copper or aluminumcoated silicon. Still other embodiments and variations may occur tothose of skill in the art. All such embodiments and variations arebelieved to be within the scope and sphere of the present invention.

1. An integrated circuit package comprising: a substrate having aplurality of conductive traces; a semiconductor die mounted on a firstsurface of said substrate; a die adapter mounted on said semiconductordie; a plurality of wire bonds between said semiconductor die and onesof said conductive traces; a heat spreader disposed proximal to andspaced from said die adapter by at least one collapsible spacer, whereinthe collapsible spacer is a substantially spherical ball; a moldingcompound encapsulating the semiconductor die, the wire bonds, the dieadapter and said collapsible spacer between the substrate and the heatspreader; and a ball grid array on a second surface of said substrate,bumps of said ball grid array being electrically connected to saidconductive traces.
 2. The integrated circuit package according to claim1, wherein said at least one collapsible spacer comprises a collapsiblespacer disposed between and in contact with said heat spreader and saiddie adapter.
 3. The integrated circuit package according to claim 1,wherein wire bonding further comprises ground wire bonding saidsemiconductor die to at least one ground pad on said substrate.
 4. Anintegrated circuit package comprising: a substrate having a plurality ofconductive traces; a semiconductor die mounted on a first surface ofsaid substrate; a die adapter mounted on said semiconductor die; aplurality of wire bonds between said semiconductor die and ones of saidconductive traces; a heat spreader disposed proximal to and spaced fromsaid die adapter by at least one collapsible spacer; a molding compoundencapsulating the semiconductor die, the wire bonds, the die adapter andsaid collapsible spacer between the substrate and the heat spreader; anda ball grid array on a second surface of said substrate, bumps of saidball grid array being electrically connected to said conductive traces,wherein said at least one collapsible spacer further comprises aplurality of collapsible spacers disposed between and in contact withsaid heat spreader and said substrate array.
 5. An integrated circuitpackage comprising: a substrate having a plurality of conductive traces;a semiconductor die mounted on a first surface of said substrate; a dieadapter mounted on said semiconductor die; a plurality of wire bondsbetween said semiconductor die and ones of said conductive traces; aheat spreader disposed proximal to and spaced from said die adapter byat least one collapsible spacer; a molding compound encapsulating thesemiconductor die, the wire bonds, the die adapter and said collapsiblespacer between the substrate and the heat spreader; and a ball gridarray on a second surface of said substrate, bumps of said ball gridarray being electrically connected to said conductive traces, whereinwire bonding further comprises ground wire bonding said semiconductordie to said die adapter.